This application claims priority under 35 U.S.C. xc2xa7119 and/or 365 to Patent Application Ser. No. 0103552-6 filed in Sweden on Oct. 24, 2001.
The present invention relates to a three-edged drill for chip forming metal machining.
During drilling, chips are produced at ta front tip end of the drill, the chips being formed and transported from the tip-forming end of the drill to the opposite end of the drill, said transportation taking place in the chip channels. During drilling with a three-edged drill, the part of the drill that first reaches the workpiece forces the tip of the drill to rotate around an axis that does not coincide with the rotational axis of the drill shank. Thus, an entrance for the desired hole is obtained that develops outside the desired entrance. An example of said type of three-edged drill is disclosed in WO 01/07189. Furthermore, it is common that the balancing of known drills is deteriorated when the drill is worn.
An object of the present invention is to provide a three-edged drill, at which balancing of the drill is not effected as the drill is worn.
Another object of the present invention is to provide a three-edged drill having a good balance before the entire drill tip is in engagement.
An additional object of the present invention is to provide a three-edged drill of good strength.
These and other objects of the present invention are realized by a drill for chip forming metalworking which comprises a shank that defines a center axis of rotation and has axial front and rear ends. The front end comprises three radially outer cutting edges spaced apart circumferentially with respect to the axis. Three chip channels extend rearwardly from respective ones of the radially outer cutting edges. Three flush channels each terminate in an axially front end of a respective chip channel for conducting flushing fluid. Each radially outer cutting edge includes an axially forwardmost portion disposed at a radially innermost end thereof. The axially forwardmost portions of the radially outer cutting edges are arranged to:
lie in a common imaginary plane oriented perpendicular to the axis,
be spaced by equal radial distances from the axis, and
lie in a common imaginary circle having a center which coincides with the axis and which intersects the three flush channels as the drill is viewed in an axial direction.